The present invention relates to a vehicle brake control system capable of producing a suitable brake operating feeling, causing electrically-driven brake units to be simultaneously actuated with excellent responsivity by detecting a brake operating condition accurately and quickly, generating sufficient and necessary braking force making up for insufficiency of brake operating force when it is needed to brake suddenly and furthermore securing the proper operation of the brake units even at the time of an electric system failure.
Intelligent braking functions have been introduced positively into recent vehicle brake equipment to install antilock brake systems and traction control systems and in order to deal with intelligent systems, the development of electric brake equipment is in progress.
In the case of such electric brake equipment, it marks a very important point whether the brake equipment is operated as a driver demands because the performance of a brake-operation detecting unit for allowing the driver to precisely detect a brake-pedal operating condition and the performance of a control unit for controlling the braking force of brake units by operating electric actuators according to a signal from the brake-operation detecting unit greatly affect the braking performance.
A conventional brake-operation detecting unit has been developed as shown in FIG. 10, for example, which is equipped, in the stepping-on portion la of a brake pedal 1 of a vehicle, with a stepping-on force sensor 2 for detecting the force of stepping on the brake pedal 1 by a driver.
A predetermined operational counterforce (a brake operating feeling) is normally obtained from the aforesaid brake pedal 1 itself when the driver steps on the brake pedal 1, which is resiliently supported by a pedal urging spring 3, so that the brake pedal 1 is restored to the initial position quickly when the driver releases his leg from the brake pedal 1.
The aforesaid stepping-on force sensor 2 is what outputs an electric signal in response to the stepping-on force applied by the driver. The stepping-on force applied by the driver to the stepping-on force sensor 2 sharply increases as shown by a curve A of FIG. 11 at the time of braking suddenly including braking in a panic, whereas it slowly increases as shown by a curve B thereof at the time of braking slowly including braking normally.
Therefore, as shown in FIG. 12, the electric signal outputted from the stepping-on force sensor 2 is differentiated to obtain an increasing rate of the stepping-on force (inclinations of the curves A, B shown in FIG. 11) in order to distinguish between suddenly braking and gradually braking. It is thus possible to realize the braking operation that the driver demands by controlling the operation of the brake units in accordance with the results thus distinguished.
Incidentally, a curve C in FIG. 12 corresponds to the curve A at the time of braking suddenly in FIG. 11, whereas a curve D in FIG. 12 corresponds to the curve B at the time of braking gradually in FIG. 11.
There has also been proposed a control unit for controlling the braking force outputted from the brake unit such that supply of electric power to the electric actuator is controlled according to the output signal of the stepping-on force sensor 2 so as to obtain braking force proportional to the intensity of the stepping-on force detected by the stepping-on force sensor 2.
As shown by the curve A of FIG. 11, noise n having a minute amplitude is carried on the stepping-on force sensor at the time of braking suddenly and when the output signal of the stepping-on force sensor 2 is differentiated, the noise n is amplified and the amplified noise n affects the stepping-on force as shown in FIG. 12. Consequently, it is feared that a wrong decision would be made on the operating condition of the brake pedal 1 (e.g., whether or not the sudden brake is applied?) because of the noise n.
When a filtering process is carried out to remove the noise n in order to avoid such inconvenience, there also develops a problem of reducing the response speed because the time required for the filtering process increases a time lag in the braking operation, though a right decision may be made on the operating condition of the brake pedal 1.
When braking force proportional to the stepping-on force detected by the stepping-on force sensor 2 is obtained by controlling the operation of the electric actuator in the case of a female driver having weak stepping-on strength, for example, the value of the stepping-on force detected by the stepping-on force sensor 2 at the time of braking suddenly is small, which may result in posing a serious problem because necessary and sufficient braking force is unavailable.
In some of the conventional electric brakes, for example, disc brakes, a driving unit is simply electrically-driven, that is, an electric motor is employed for moving back and forth a piston for pressing brake pads against a disc and the problem in this case is that the braking operation is hardly securable at the time of an electric system failure.